Semiconductor light emitting device

ABSTRACT

A semiconductor light emitting device includes a multi-quantum-well structure, a first capping layer, a second capping layer, and an electron barrier layer stacked in order. The multi-quantum-well structure includes a plurality of alternately-stacked potential barrier layers and potential well layers. The first capping layer is a semiconductor layer, and the second capping layer is a p-doped semiconductor layer. Each of the first and second capping layers has an aluminum mole fraction larger than that of each of the potential barrier layers, and the aluminum mole fraction of the first capping layer is larger than that of at least a portion of the electron barrier layer. A method for preparing the semiconductor light emitting device is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 17/209,485, filed on Mar. 23, 2021, which is acontinuation-in-part (CIP) of U.S. patent application Ser. No.16/716,598, filed on Dec. 17, 2019, which is a CIP of U.S. patentapplication Ser. No. 16/426,016, filed on May 30, 2019, which is a CIPof International Application No. PCT/CN2018/078654, filed on Mar. 12,2018, which claims priority to Chinese Invention Patent Application No.201710638217.9, filed on Jul. 31, 2017. The entire content of each ofthe U.S. and Taiwanese patent applications is incorporated herein byreference.

FIELD

The disclosure relates to a semiconductor device, and more particularlyto a semiconductor light emitting device and a method for preparing thesame.

BACKGROUND

A gallium nitride (GaN)-based light emitting diode (LED) includes ap-type semiconductor layer providing electron holes and an n-typesemiconductor layer providing electrons, having between them a P-Njunction that converts electrical energy to luminous energy. Whenelectric current passes through the LED in the forward direction, theelectrons provided by the n-type semiconductor layer recombines with theelectron holes in the p-type semiconductor layer, releasing energycorresponding to the band gap between the conduction band and thevalence band. The energy released may either be thermal energy or light,and the light may be emitted outwards.

However, when epitaxially growing the p-type semiconductor layer, growthconditions such as the growth temperature may cause a p-type dopant(e.g. magnesium) to spread to a quantum well structure, thus negativelyaffecting the material quality of a potential well layer in the quantumwell structure. This may, in turn, lower the luminous efficiency of theLED. In addition, how to reduce electron overflow and electron tunnelingeffect between the n-type semiconductor layer and the p-typesemiconductor layer remains a problem to be solved.

SUMMARY

Therefore, the object of the disclosure is to provide a semiconductorlight emitting device that can alleviate the drawback of the prior art.A method for preparing the semiconductor light emitting device is alsoprovided.

According to one aspect of the disclosure, a semiconductor lightemitting device includes an n-type semiconductor layer, amulti-quantum-well structure, a first capping layer, a second cappinglayer, an electron barrier layer, a p-type semiconductor layer, and ap-type contact layer stacked in order.

The multi-quantum-well structure includes a plurality ofalternately-stacked potential barrier layers and potential well layers.

The first capping layer is one of an undoped semiconductor layer and ap-doped semiconductor layer, and the second capping layer is a p-dopedsemiconductor layer. The second capping layer is directly formed on thefirst capping layer. Each of the first and second capping layers has analuminum mole fraction larger than that of each of the potential barrierlayers, and the aluminum mole fraction of the first capping layer islarger than that of at least a portion of the electron barrier layer.

According to another aspect of the disclosure, a method for preparing asemiconductor light emitting device includes:

growing an n-type semiconductor layer on a growth substrate;

growing a multi-quantum-well structure on the n-type semiconductorlayer, the multi-quantum-well structure including a plurality ofalternately stacked potential barrier layers and potential well layers;

growing a first capping layer on the multi-quantum-well structure, thefirst capping layer being an undoped layer;

growing directly on the first capping layer a second capping layer, thesecond capping layer being a p-doped layer with a p-type dopant; and

growing an electron barrier layer on the second capping layer; and

growing sequentially a p-type semiconductor layer and a p-type contactlayer on the electron barrier layer.

The first capping layer has a growth temperature between that of thepotential barrier layers and that of the potential well layers. Thesecond capping layer has a growth temperature lower than that of thepotential well layers. Each of the first and second capping layers hasan aluminum mole fraction larger than that of each of the potentialbarrier layers, and the aluminum mole fraction of the first cappinglayer is larger than that of at least a portion of the electron barrierlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the disclosure will become apparent inthe following detailed description of the embodiment with reference tothe accompanying drawings, of which:

FIG. 1 is a fragmentary schematic sectional view of a first embodimentof a semiconductor light emitting device according to the disclosure;

FIG. 2 is a fragmentary schematic sectional view of a second embodimentof a semiconductor light emitting device according to the disclosure;

FIG. 3 is a fragmentary schematic sectional view of a third embodimentof a semiconductor light emitting device according to the disclosure;

FIG. 4 is a fragmentary schematic sectional view of a fourth embodimentof a semiconductor light emitting device according to the disclosure;and

FIG. 5 is a process flow diagram of an embodiment of a method ofpreparing a semiconductor light emitting device according to thedisclosure.

DETAILED DESCRIPTION

Referring to FIG. 1 , a first embodiment of a semiconductor lightemitting device according to the disclosure includes a growth substrate100, and an n-type semiconductor layer 200, a multi-quantum-wellstructure 300, a first potential barrier layer 310, a first cappinglayer 410, a second capping layer 420, an electron barrier layer 500, ap-type semiconductor layer 600, and a p-type contact layer 700 stackedin order on the growth substrate 100.

The growth substrate 100 may be made of one of sapphire, gallium nitride(GaN), and silicon, but is not limited in this respect.

In certain embodiments, in order to reduce the strain caused by latticemismatch between the growth substrate 100 and the n-type semiconductorlayer 200, the semiconductor light emitting device may further include abuffer layer 800 formed between the n-type semiconductor layer 200 andthe growth substrate 100. A material for making the buffer layer 800 isselected from the group consisting of aluminum nitride (AlN), GaN,aluminum gallium nitride (AlGaN), aluminum indium gallium nitride(AlInGaN), indium nitride (InN), indium gallium nitride (InGaN), andcombinations thereof. In certain embodiments, the buffer layer 800 maybe an Al_(1-x)Ga_(x)In_(y)N layer, wherein x and y represent molefractions, 0≤x<1 and 0≤y<1.

The multi-quantum-well structure 300 includes a plurality ofalternately-stacked second potential barrier layers 301 and potentialwell layers 302. The repetition period of a combination of one of thesecond potential barriers layers 301 and one of the potential welllayers 302 of the multi-quantum-well structure 300 is between 3 and 20.The band gap of each of the second potential barrier layers 301 islarger than that of each of the potential well layers 302. Each of thesecond potential barrier layers 301 is one of an undoped semiconductorlayer and an n-doped semiconductor layer.

The first potential barrier layer 310 is an undoped semiconductor layerhaving one of a single-layer structure and a multi-layered structure. Incertain embodiments, the first potential barrier layer 310 may be anundoped GaN (u-GaN) layer, an undoped AlGaN (u-AlGaN) layer, au-GaN/u-AlGaN multi-layered structure, or an undoped InGaN/undopedAlInGaN/u-AlGaN multi-layered structure.

The first capping layer 410 is formed for reducing the spreading ofp-type doping materials in the second capping layer 420, the electronbarrier layer 500 and the p-type semiconductor layer 600 to themulti-quantum-well structure 300 which may cause a reduction of theluminous efficiency of the semiconductor light emitting device. Thefirst capping layer 410 may be an undoped semiconductor layer. However,in certain embodiments, the first capping layer 410 may be a p-dopedsemiconductor layer which is formed due to diffusion of a p-type dopantin the second capping layer 420. Specifically, the first capping layer410 is intended to be undoped, but due to the possible epitaxial defectsin the first capping layer 410, the p-type dopant in the second cappinglayer 420 may diffuse into the first capping layer 410 and dope thefirst capping layer 410.

The second capping layer 420 is a p-doped semiconductor layer doped withthe p-type dopant as mentioned above. The second capping layer 420 isdirectly formed on the first capping layer 410. The second capping layer420 has a p-type doping concentration higher than that of the p-typesemiconductor layer 600 and lower than that of the p-type contact layer700. The high level of p-type doping increases electron hole injectioneffect and allows the second capping layer 420 to act as a holeinjection layer. Specifically, the second capping layer 420 has a p-typedoping concentration ranging between 1×10¹⁹ cm⁻³ and 5×10²⁰ cm⁻³. Incertain embodiments, the second capping layer 420 has a p-type dopingconcentration ranging between 5×10¹⁹ cm⁻³ and 2×10²⁰ cm⁻³. The secondcapping layer 420 has a thickness larger than that of each of thepotential well layers 302 of the multi-quantum-well structure 300.Specifically, the second capping layer 420 has a thickness less than 40nm.

Each of the first and second capping layers 410, 420 have a band gaplarger than that of each of the second potential barrier layers 301. Thesecond capping layer 420 has a band gap not larger than the electronbarrier layer 500. The larger band gap of each of the first and secondcapping layers 410, 420 reduces the electron overflow and increases thehole injection effect.

In certain embodiments, the first capping layer 410 is an undopedAl_(x)N layer or a p-doped Al_(x)N layer, wherein x represents aluminummole fraction and x=1; the second capping layer 420 is a p-dopedAl_(x)Ga_((1-x))N layer, wherein x represents aluminum mole fraction.The aluminum mole fraction of the first capping layer 410 is larger thanthat of the second capping layer 420.

Each of said first and second capping layers 410, 420 has an aluminummole fraction that is larger than that of each of the second potentialbarrier layers 301. The aluminum mole fraction of the first cappinglayer 410 is larger than that of at least a portion of the electronbarrier layer 500. In the first embodiment, the aluminum mole fractionof the first capping layer 410 is larger than that of the electronbarrier layer 500.

In the first embodiment, the electron barrier layer 500 is anAlGaN-containing layer having an aluminum mole fraction ranging from0.02 to 0.25, which is less than that of the first capping layer 410. Tobe specific, the electron barrier layer 500 is an Al_(x)Ga_((1-x))Nlayer, wherein 0.02≤x≤0.25, and may be doped with p-type impurity usingion implantation technique. In this embodiment, the electron barrierlayer 500 has an aluminum content which decreases in a direction fromthe multi-quantum-well structure 300 to the p-type contact layer 700.

In certain embodiments, the second capping layer 420 is anAlGaInN-containing layer having an aluminum mole fraction not largerthan that of the electron barrier layer 500. To be specific, the secondcapping layer 420 is an Al_(x)Ga_((1-x))In_(y)N layer, wherein x and yrepresent mole fractions, 0≤x<1 and 0≤y<1. However, since the secondcapping layer 420 has a thickness larger than that of the electronblocking layer 500, a total aluminum content of the second capping layer420 is larger than that of the electron blocking layer 500.

Referring to FIG. 2 , a second embodiment of the semiconductor lightemitting device according to the disclosure is shown to be generallysimilar to the first embodiment, except that in the second embodiment,the electron barrier layer 500 includes a first electron barriersublayer 500-1 and a second electron barrier sublayer 500-2 that aresequentially formed on the second capping layer 420 in such order. Inthe second embodiment, the first electron barrier sublayer 500-1 is anAlN-containing sublayer. The first electron barrier sublayer 500-1 maybe an Al_(x)N layer, wherein x=1. The second electron barrier sublayer500-2 is an AlGaN-containing sublayer. The second electron barriersublayer 500-2 may be an Al_(x)Ga_(1-x)N layer, wherein 0<x≤0.35. Thesecond electron barrier sublayer 500-2 has a thickness larger than thatof the first electron barrier sublayer 500-1. The first electron barriersublayer 500-1 has an aluminum mole fraction that is higher than that ofthe second electron barrier sublayer 500-2. The first capping layer 410has an aluminum mole fraction that is larger than that of the secondelectron barrier sublayer 500-2.

Referring to FIG. 3 , a third embodiment of the semiconductor lightemitting device according to the disclosure is shown to be generallysimilar to the second embodiment, except that in the third embodiment,the second electron barrier sublayer 500-2 and the first electronbarrier sublayer 500-1 are sequentially formed on the second cappinglayer 420 in such order.

Referring to FIG. 4 , a fourth embodiment of the semiconductor lightemitting device according to the disclosure is shown to be generallysimilar to the second embodiment, except that in the fourth embodiment,the electron barrier layer 500 further includes a third electron barriersublayer 500-3 formed on the second electron barrier sublayer 500-2opposite to the first electron barrier sublayer 500-1. In the fourthembodiment, the third electron barrier sublayer 500-3 is anAlN-containing sublayer that has a thickness and an aluminum molefraction similar to those of the first electron barrier sublayer 500-1.To be specific, the third electron barrier sublayer 500-3 may be anAl_(x)N layer, wherein x=1. Each of the first and third electron barriersublayers 500-1, 500-3 has an aluminum mole fraction larger than that ofthe second electron barrier sublayer 500-2, and the aluminum molefraction of the first capping layer 410 is larger than that of thesecond electron barrier sublayer 500-2. In addition, each of the firstand third electron barrier sublayers 500-1, 500-3 has a thickness lessthan that of the second electron barrier sublayer 500-2, and at leastone of the first and third electron barrier sublayers 500-1, 500-3 has athickness less than 5 nm.

Referring to FIG. 5 , an embodiment of a method for preparing the firstembodiment of the semiconductor light emitting device of the presentdisclosure includes growing the n-type semiconductor layer 200 on thegrowth substrate 100, growing the multi-quantum-well structure 300including a plurality of alternately stacked second potential barrierlayers 301 and potential well layers 302 on the n-type semiconductorlayer 200, growing the first potential barrier layer 310 on themulti-quantum-well structure 300, growing the first capping layer 410being an undoped layer on top of the first potential barrier layer 310,growing the second capping layer 420 being a p-doped layer with a p-typedopant directly on the first capping layer 410, growing the electronbarrier layer 500 on the second capping layer 420, and growingsequentially the p-type semiconductor layer 600 and the p-type contactlayer 700 on the electron barrier layer 500.

For certain embodiments, in which the first capping layer 410 hasepitaxial defects, during growth of the second capping layer 420, thep-type dopant may diffuse into the first capping layer 410 so that thefirst capping layer 410 becomes a p-doped semiconductor layer.

The n-type semiconductor layer 200, the multi-quantum-well structure300, the first capping layer 410, the second capping layer 420, theelectron barrier layer 500, the p-type semiconductor layer 600 and thep-type contact layer 700 are grown using epitaxial technique.

In certain embodiments, the method further includes growing the bufferlayer 800 on the growth substrate 100 before growth of the n-typesemiconductor layer 200.

Each of the potential well layers 302 has a growth temperature lowerthan that of each of the second potential barrier layers 301. The firstpotential barrier layer 310 has a growth temperature equal to that ofeach of the second potential barrier layers 301.

The first capping layer 410 has a growth temperature between that of thesecond potential barrier layers 301 and that of the potential welllayers 302, and the second capping layer 420 has a growth temperaturelower than that of the potential well layers 302. The low growthtemperature of each of the first and second capping layers 410, 420relative to the second potential barrier layers 301 prevents lowering ofthe crystal quality of the multi-quantum-well structure 300 andspreading of the p-type impurity. However, the quality of the first andsecond capping layer 410, 420, especially the second capping layer 420whose growth temperature is lower than that of each of the potentialwell layers 302, may be negatively affected by the lower growthtemperature, and thus the second capping layer 420 has a thickness lessthan 40 nm. However, the thickness of the second capping layer 420 mayaffect the properties of the light emitting device and should becontrolled within a desired range. In certain embodiments, the thicknessof the second capping layer 420 is between 200 Å to 350 Å, and thethickness of the first capping layer 410 is between 2 Å to 10 Å.

The method for preparing the second embodiment of the semiconductorlight emitting device of the present disclosure is generally similar tothat for preparing the first embodiment of the semiconductor lightemitting device, except that the electron barrier layer 500 is grown byfirst growing the first electron barrier sublayer 500-1 on the secondcapping layer 420 and then growing the second electron barrier sublayer500-2 on the first electron barrier sublayer 500-1.

The method for preparing the third embodiment of the semiconductor lightemitting device of the present disclosure is generally similar to thatfor preparing the second embodiment of the light emitting device, exceptthat the electron barrier layer 500 is grown by first growing the secondelectron barrier sublayer 500-2 on the second capping layer 420 and thengrowing the first electron barrier sublayer 500-1 on the second electronbarrier sublayer 500-2.

The method for preparing the fourth embodiment of the semiconductorlight emitting device of the present disclosure is generally similar tothat for preparing the second embodiment of the light emitting device,except that the step of growing the electron barrier layer 500 furtherincludes growing the third electron barrier sublayer 500-3 on the secondelectron barrier sublayer 500-2.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiment. It will be apparent, however, to oneskilled in the art, that one or more other embodiments may be practicedwithout some of these specific details. It should also be appreciatedthat reference throughout this specification to “one embodiment,” “anembodiment,” an embodiment with an indication of an ordinal number andso forth means that a particular feature, structure, or characteristicmay be included in the practice of the disclosure. It should be furtherappreciated that in the description, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure and aiding in theunderstanding of various inventive aspects, and that one or morefeatures or specific details from one embodiment may be practicedtogether with one or more features or specific details from anotherembodiment, where appropriate, in the practice of the disclosure.

While the disclosure has been described in connection with what isconsidered the exemplary embodiment, it is understood that thisdisclosure is not limited to the disclosed embodiment but is intended tocover various arrangements included within the spirit and scope of thebroadest interpretation so as to encompass all such modifications andequivalent arrangements.

What is claimed is:
 1. A semiconductor light emitting device,comprising: an n-type semiconductor layer, a multi-quantum-wellstructure, a first capping layer, a second capping layer, an electronbarrier layer, a p-type semiconductor layer, and a p-type contact layerstacked in order, wherein said multi-quantum-well structure includes aplurality of alternately-stacked potential barrier layers and potentialwell layers; wherein said first capping layer is one of an undopedsemiconductor layer and a p-doped semiconductor layer, said secondcapping layer being a p-doped semiconductor layer; wherein said firstcapping layer has an aluminum mole fraction larger than that of each ofsaid potential barrier layers; and wherein said electron barrier layerincludes a first electron barrier sublayer and a second electron barriersublayer, and the aluminum mole fraction of said first capping layerbeing larger than that of said second electron barrier sublayer.
 2. Thesemiconductor light emitting device as claimed in claim 1, wherein saidfirst electron barrier sublayer and said second electron barriersublayer are sequentially formed on said second capping layer in suchorder.
 3. The semiconductor light emitting device as claimed in claim 1,wherein said second electron barrier sublayer and said first electronbarrier sublayer are sequentially formed on said second capping layer insuch order.
 4. The semiconductor light emitting device as claimed inclaim 3, wherein said first electron barrier sublayer has a thicknessless than that of said second electron barrier sublayer.
 5. Thesemiconductor light emitting device as claimed in claim 1, wherein saidelectron barrier layer further includes a third electron barriersublayer formed on said second electron barrier sublayer opposite tosaid first electron barrier sublayer.
 6. The semiconductor lightemitting device as claimed in claim 5, wherein each of said first andthird electron barrier sublayers has a thickness less than that of saidsecond electron barrier sublayer.
 7. The semiconductor light emittingdevice as claimed in claim 1, wherein said second electron barriersublayer has a thickness larger than that of said first electron barriersublayer.
 8. The semiconductor light emitting device as claimed in claim1, wherein said electron barrier layer has an aluminum mole fraction notless than that of said second capping layer.
 9. The semiconductor lightemitting device as claimed in claim 1, wherein the aluminum molefraction of said first capping layer is larger than that of said secondcapping layer.
 10. The semiconductor light emitting device as claimed inclaim 1, wherein said second capping layer has a thickness larger thanthat of each of said potential well layers of said multi-quantum-wellstructure.
 11. The semiconductor light emitting device as claimed inclaim 1, wherein said second capping layer has a p-type dopingconcentration higher than that of said p-type semiconductor layer andlower than that of said p-type contact layer.
 12. The semiconductorlight emitting device as claimed in claim 1, wherein said second cappinglayer has a p-type doping concentration between 1×¹⁹ cm⁻³ and 5×10²⁰cm⁻³.
 13. The semiconductor light emitting device as claimed in claim 1,wherein said second capping layer has a thickness less than 40 nm. 14.The semiconductor light emitting device as claimed in claim 1, whereinsaid second capping layer is an aluminum gallium indium nitride(AlGaInN)-containing layer.
 15. The semiconductor light emitting deviceas claimed in claim 14, wherein said second capping layer has analuminum mole fraction not larger than that of said electron barrierlayer.
 16. The semiconductor light emitting device as claimed in claim1, further comprising a growth substrate formed on said n-typesemiconductor layer opposite to said multi-quantum-well structure. 17.The semiconductor light emitting device as claimed in claim 1, whereineach of said potential barrier layers is one of an undoped semiconductorlayer and an n-doped semiconductor layer.
 18. The semiconductor lightemitting device as claimed in claim 1, wherein said electron barrierlayer further includes a third electron barrier sublayer formed on saidsecond electron barrier sublayer opposite to said first electron barriersublayer, at least one of said first and third electron barriersublayers having a thickness less than 5 nm.
 19. The semiconductor lightemitting device as claimed in claim 16, further comprising a bufferlayer formed between said n-type semiconductor layer and said growthsubstrate, said buffer layer being made from a material selected fromthe group consisting of AlN, gallium nitride (GaN), AlGaN, aluminumindium gallium nitride (AlInGaN), indium nitride (InN), indium galliumnitride (InGaN) and combinations thereof.